Washington (CNN) -- One of two photojournalists killed in a 2007 attack by a U.S. helicopter gunship in Iraq was being rescued when the gunship's crew fired on the van to which he was being carried, according to footage posted online Monday.

Reuters photographer Saeed Cmagh survived an initial strafing by the Apache gunship's 30 mm machine gun, but he apparently died when the gunship opened fire on people attempting to get him off the sidewalk where he lay, according to the video. The aerial footage was posted by the Web site WikiLeaks, which said the video remains classified and "clearly shows the unprovoked slaying of a wounded Reuters employee and his rescuers."

WikiLeaks is a site that publishes anonymously submitted documents, video and other sensitive materials.

The gunship's crew requested and received permission to open fire on the van, which the crew believed was trying to evacuate wounded insurgents, the U.S. military later concluded.

Chmagh's Reuters colleague, Namir Noor-Eldeen, also died in the July 2007 air strike in the New Baghdad district of the Iraqi capital. Noor-Eldeen appears to have been killed in the first round of strafing from the gunship.

The U.S. investigation into the attack found that the helicopter gunship's crew mistook the journalists' cameras for weapons while seeking out insurgents who had been firing at American troops in the area. The fliers estimated they killed 12 to 15 Iraqis in the attack.

"This tragic incident was investigated at that time by the brigade involved and the investigation found that the forces involved were not aware of the presence of the two reporters, and that all evidence available supported the conclusion by those forces that they were engaging armed insurgents, and not civilians," Maj. Shawn Turner, a U.S. military spokesman, told CNN in a written statement Monday.

The Army's 2007 report on the incident found the crew had "neither reason nor probability to assume that neutral media personnel were embedded with enemy forces," according to a copy of the document released to CNN.

"We regret the loss of innocent life, but this incident was promptly investigated, and there was never any attempt to cover up any aspects of this engagement," Turner added.

A total of 139 journalists, nearly 120 of them Iraqis, have been killed during the 7-year-old war, according to the Committee To Protect Journalists. Reuters said the deaths of Chmagh and Noor-Eldeen "were tragic and emblematic of the extreme dangers that exist in covering war zones."

"This footage is deeply disturbing and reminds us of what journalists in war zones undergo to bring us the news," Joel Simon, the group's executive director, said in a written statement. "The video also confirms our long-held view that a thorough and transparent investigation into this incident is urgently needed."

And Reuters said the deaths of Chmagh and Noor-Eldeen "were tragic and emblematic of the extreme dangers that exist in covering war zones."

"We continue to work for journalist safety and call on all involved parties to recognise the important work that journalists do and the extreme danger that photographers and video journalists face in particular," David Schlesinger, the wire service's editor-in-chief, said in a statement released to CNN.

"The video released today via WikiLeaks is graphic evidence of the dangers involved in war journalism and the tragedies that can result."